There have been well-known sliding contact component having flat or circular cylindrical geometry, configured by stacking resin work materials each composed of cotton fabric, as a reinforcing base, impregnated with a thermosetting synthetic resin such as phenolic resin and epoxy resin, or with a resin composition composed of the thermosetting resin added with polytetrafluoroethylene resin (Patent Document 1). The sliding contact component are adopted in a wide variety of fields, including wear ring fitted to the outer circumferential surface of piston of hydraulic cylinder, underwater slide bearing and so forth, by virtue of its excellence in the wear resistance, load resistance and rigidity. In particular, excellent performances of the phenolic resin under water lubrication are largely ascribable to the surface characteristics thereof, and are also possibly contributed by adsorption of water to the cotton fabric used as the base, and good affinity of OH group of the phenolic resin with water.
The circular cylindrical multi-layered sliding contact component manufactured using the fiber-reinforced resin composition composed of the cotton fabric and the phenolic resin has, however, been facing difficulty in keeping a constant clearance (gap of sliding contact) with respect to the opposing shaft, when used in a humid atmosphere or underwater, due to swelling and dimensional changes as a consequence. Such swelling of the circular cylindrical multi-layered sliding contact component is mainly ascribable to high water absorptivity of the cotton fabric used as the reinforcing base. Accordingly, low-water-absorptive synthetic fiber fabrics, composed of polyester fiber, polyacrylonitrile fiber and so forth, have attracted public attention as reinforcing bases other than the cotton fabric, intended for underwater applications. The synthetic fiber fabrics are advantageous also in that they are relatively inexpensive, and express reinforcing effects on resins.
The synthetic resins having these advantages, however, suffer from their poor adhesiveness to resins, when intended to achieve a satisfactory level of reinforcing effect with respect to the resins.
Patent Document 2 discloses a fiber-reinforced resin composition configured by using, as a reinforcing material, a woven fabric made of polyamide fiber, polyester fiber, polyacrylonitrile fiber or carbon fiber, and impregnated with a thermosetting synthetic resin such as phenolic resin added with fluorine-containing polymer, melamine resin, epoxy resin or alkyd resin, and a slide bearing using the same. In order to improve the adhesiveness between these synthetic fibers and the synthetic resins, the synthetic resins are added with co-condensation products of polyamide and polyvinyl alcohol derivatives, as adhesion enhancers.
Patent Document 3 discloses a reinforced plastic plate configured by stacking sheets of polyester fiber woven fabric, used as reinforcing bases, after being impregnated with an unsaturated polyester resin. It is, however, difficult to adhere the intact polyester fiber to the unsaturated polyester resin, due to a poor content of functional groups in the polyester fiber. The Patent Document 3 therefore describes that, in order to improve the adhesiveness, or affinity, of the fiber with the resin, the polyester fiber is annealed with a bisphenol-based epoxy resin adhesive in an organic solvent, at a temperature of 150° C. or below for 5 to 120 minutes.
Non-Patent Document 1 discloses a technique of a surface treatment for polyester fiber described below, aiming at improving interfacial adhesiveness between a polyester fiber woven fabric as a base and a resin as a matrix in a composite material.
(1) Chemical treatment for improving wettability with RFL (resolcinol folmaldehyde latex), for imparting reactivity, and for improving adhesiveness, by increasing the number of carboxyl groups, hydroxy groups, and amide groups, making use of property of polyester fiber susceptible to hydrolysis, amine-assisted decomposition, alcohol-assisted decomposition, and so forth.
(2) Physical treatment using electron beam, ultraviolet radiation, or low-temperature plasma.
(3) Surface treatment using isocyanate compounds.
(4) Surface treatment using ethylene urea, ethylene urethane, phenyl urethane or the like.
(5) Surface treatment using alkali.
Problems in the above-described techniques of surface treatment for synthetic fibers disclosed in Patent Document 2, Patent Document 3 and Non-Patent Document 1 are enumerated below:
(1) poor workability and very strong toxicity in some cases;
(2) treatment liquid is readily affected by temperature and humidity, and less stable;
(3) high cost due to need of large volume of treatment liquid; and
(4) the synthetic fibers per se are degraded in some cases.
It is therefore understood that no techniques, capable of obtaining sufficient levels of improvement in the adhesiveness and safety, have been established as the methods of surface treatment of synthetic fibers.